linux-ext4 - Re: EXT4 is ~2X as slow as XFS (593MB/s vs 304MB/s) for writes?

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Date:	Sat, 27 Feb 2010 06:36:37 -0500 (EST)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	Eric Sandeen <sandeen@...hat.com>
cc:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alan Piszcz <ap@...arrain.com>
Subject: Re: EXT4 is ~2X as slow as XFS (593MB/s vs 304MB/s) for writes?



On Sat, 27 Feb 2010, Justin Piszcz wrote:

> 
> 
> On Sat, 27 Feb 2010, Justin Piszcz wrote:
> 
> > 
> > 
> > On Sat, 27 Feb 2010, Justin Piszcz wrote:
> > 
> > > 
> > > 
> > > On Fri, 26 Feb 2010, Eric Sandeen wrote:
> > >
> 
> Hi,
> 
> I have found the same results on 2 different systems:
> 
> It seems to peak at ~350MiB/s performance on mdadm raid, whether
> a RAID-5 or RAID-0 (two separate machines):
> 
> The only option I found that allows it to go from:
> 10737418240 bytes (11 GB) copied, 48.7335 s, 220 MB/s
> to
> 10737418240 bytes (11 GB) copied, 30.5425 s, 352 MB/s
> 
> Is the -o nodelalloc option.
> 
> How come it is not breaking the 350MiB/s barrier is the question?
> 
> Justin.
> 
>

Besides large sequential I/O, ext4 seems to be MUCH faster than XFS when
working with many small files.

EXT4

p63:/r1# sync; /usr/bin/time bash -c 'tar xf linux-2.6.33.tar; sync'
0.18user 2.43system 0:02.86elapsed 91%CPU (0avgtext+0avgdata 5216maxresident)k
0inputs+0outputs (0major+971minor)pagefaults 0swaps
linux-2.6.33  linux-2.6.33.tar
p63:/r1# sync; /usr/bin/time bash -c 'rm -rf linux-2.6.33; sync'
0.02user 0.98system 0:01.03elapsed 97%CPU (0avgtext+0avgdata 5216maxresident)k
0inputs+0outputs (0major+865minor)pagefaults 0swaps

XFS

p63:/r1# sync; /usr/bin/time bash -c 'tar xf linux-2.6.33.tar; sync'
0.20user 2.62system 1:03.90elapsed 4%CPU (0avgtext+0avgdata 5200maxresident)k
0inputs+0outputs (0major+970minor)pagefaults 0swaps
p63:/r1# sync; /usr/bin/time bash -c 'rm -rf linux-2.6.33; sync'
0.03user 2.02system 0:29.04elapsed 7%CPU (0avgtext+0avgdata 5200maxresident)k
0inputs+0outputs (0major+864minor)pagefaults 0swaps

So I guess that's the tradeoff, for massive I/O you should use XFS, else,
use EXT4?

I still would like to know however, why 350MiB/s seems to be the maximum
performance I can get from two different md raids (that easily do 600MiB/s
with XFS).

Is this a performance issue within ext4 and md-raid?
The problem does not exist with xfs and md-raid.

Justin.


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